Ozone is a chemical agent used in industrial oxidation, water and air treatment and in may chemical syntheses. Ozone is an unstable gas, which is produced by the disassociation-association of oxygen in an electric field derived from a high voltage alternating sinusoidal current operating at frequencies typically between about 60 and 5000 Hz and voltages frequently above 20 kilovolts. Ozone generators create the electric field by corona discharge between an electrode and opposing electrode with intervening dielectric.
A tubular type generator 10 is shown in FIG. 1 and is described in Chamblee et al., U.S. Pat. No. 5,552,125. The generator 10 includes a tubular inner electrode 11 and an outer tubular electrode 13 concentric with the inner electrode 11 and mounted so as to define an annular flow path 12 for oxygen containing gas between the electrodes 11, 13. The inner electrode 11 is coated with a dielectric 14 on a surface between the inner 11 and outer 13 electrodes. The inner electrode 11 includes a hollow interior 15 for the passage of coolant. The inner electrode 11 is connected to a voltage source 16 by a high voltage line and the outer electrode is grounded.
An oxygen containing gas (O.sub.2) flows into the annular path 12 between the dielectric 14 and outer electrode 13 where a corona discharge between the electrodes 11, 13 converts some oxygen to ozone (O.sub.3). The discharge also generates heat. The heat suppresses ozone generation by converting some product ozone back to oxygen. A coolant 17 is passed into the hollow interior 15 of the inner electrode 11 to prevent heat buildup and consequential loss of product ozone. However, ozone is produced on the interior (inside diameter) of the inner electrode 11, particularly at and near the connection of the high voltage line. The coolant gas can sweep ozone from the interior 15 of the inner electrode 11 into the work area 18. Ozone is a gas that is environmentally deleterious in closed work areas. Sweeping the interior 15 of the inner electrode 11 with a cooling fluid creates an environmental hazard to workers in the vicinity of the ozone generator.
Another type of ozone generator is shown in FIG. 2, which is reproduced from Conrad et al., U.S. Pat. No. 5,630,990. In FIG. 2, tubular generator 20 includes a first electrode 25 and a second, larger diameter, electrode 26. Electrode 25 has a layer of dielectric material 27 disposed on the surface thereof and is positioned within electrode 26 to form a gap 28. A flow of feed oxygen or oxygen enriched air is directed as shown by the top arrows into a longitudinal spacing between tubular electrode 25/dielectric 27 and thence as illustrated by the arrows, to discharge gap 28 between tubular electrode 26 and concentric electrode 25/dielectric 27, thence to an exit port near the entry port of the flow of feed oxygen or oxygen enriched air. Heat and ozone produced on the surface of the inside diameter of electrode 25/dielectric 27 are swept by the feed oxygen/oxygen enriched air as a part of the charge to the discharge gap 28.
The tubular generator of the invention is characterized by a design that achieves improved dissipation of heat and ozone without undesirable discharge into the atmosphere. In one embodiment, the inventive generator is fitted with a transparent cap to permit direct observation of the corona discharge. Observation of the corona discharge permits immediate identification of electrode defects. The ozone generator of the present invention is characterized by a sealed end dielectric tube that allows flow path control of feed gas and permits visual observation of an interior electrode to assure that the interior electrode is properly operating. The ozone generator of the invention permits direct injection of product ozone into a reaction vessel for industrial oxidations, treatments or chemical syntheses.